This is was recently announced by Google that they have included site performance (site speed) in their search ranking algorithm. This means if user request a site and if give quick response and open quickly then its chance for getting in top position will be high compare to other competitors websites that take long time to load.
So, from now webmasters need to worry about the design, development, scripts, images, etc. Fast loading websites give better user experience and keep them happy. User stay more on quick loading site then slow websites. Google use variety of factors and sources to determine website speed compare to other websites and depends on that quick loading site get higher position compare to slow websites.
You can download Yahoo YSlow that help you in optimizing your website speed.
Webmasters get ready for this new change in ranking algorithm and start thinking about how to compress the web page size and improve loading time.